In the field of door jamb construction for a wide variety of different door types and uses, it has been a common practice to configure the two legs of the jamb differently for left and right hand doors and also differently depending upon whether the door swings toward or away from a room to which it is joined. That is, the two legs of the jamb each have a vertical door stop strip centrally positioned on their inner facing surfaces. These legs are located adjacent to a wall end surface on each side of a door opening and support a head piece or "header" at the top of the door. Each door jamb leg must therefore have a "dado" or offset shelf region at their tops for receiving the header in smooth and flush engagement as is well known. Then, depending upon whether the door is left handed or right handed and further depending upon whether the door is to swing inwardly or outwardly of the room to which it is attached, one leg of the jamb must be constructed to have receptacles for the door hinges located on a specified side of the vertical door stop strip and the other door jamb leg must be constructed so that the receptacle for the striker plate is also located on a specified side of the vertical door stop strip. This receptacle placement requirement in turn meant that two differently constructed door jamb legs were required for door hinge mounting and two differently constructed door jamb legs were required for door striker plate mounting.
The above requirements for both right handed and left handed differently configured jamb legs to accommodate the four (4) possible modes of door operation meant the per se expensive requirement for providing four (4) different jamb leg configurations for receiving the door hinges and striker plate on both sides of the vertical door stop strip. Furthermore, in large construction projects which might require, for example, six hundred (600) right hand doors and three hundred (300) left hand doors, the correct number of right handed and left handed door jamb legs always had to be sorted out and furnished to the construction site. The latter requirement, in turn, served to increase the cost and manpower for sorting and marshalling the correct type of door jamb legs necessary to complete a given construction project.